Pin-Box Connector Thread Segmentation for Expansion Stress Relief
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Solution Overview
Problem
Existing methods for expanding well tubulars interconnected by pin-box assemblies often result in high stresses that can lead to thread leakage or failure due to the mechanical or hydraulic expansion process.
Innovation Solution
The method involves configuring the pin and box connector members with intermeshing screw thread profiles, where the box connector member has at least one thread that does not engage a thread on the pin connector member, and introducing an axial gap or swellable dope to optimize expansion, reducing stress and enhancing sealing integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional pin-box connector assemblies with fully engaged screw threads are used for expanding well tubulars, then strong mechanical connection is achieved, but high stresses during expansion cause thread leakage and failure
Solution Approach 1:
The screw thread engagement is segmented into two distinct zones: a first portion with engaged threads providing mechanical connection, and a second portion with disengaged threads allowing stress relief. This segmentation enables the connector to maintain structural integrity while avoiding stress concentration at the thread interface during expansion.
Solution Approach 2:
Different portions of the screw thread assembly are given different functional qualities: the first portion is designed for load-bearing mechanical engagement, while the second portion is designed with clearance to accommodate expansion stresses. This local differentiation allows each zone to perform its specific function optimally without compromising the other.
2Shape
If expansion cone is pulled or pushed through interconnected tubulars, then radial expansion is achieved, but high stresses are generated in the connector assembly
Solution Approach 1:
The harmful stress concentration effect is extracted and isolated to the disengaged thread portion, which is specifically designed to accommodate expansion movements. By removing the constraint of full thread engagement, the system allows stress to be absorbed in a controlled manner without transmitting it to the critical sealing interfaces.
Solution Approach 2:
The disengaged thread portion acts as a pre-designed stress cushion that absorbs expansion forces before they can reach the engaged thread sections. This beforehand cushioning prevents stress buildup that would otherwise lead to thread leakage or connector failure during the expansion process.
3Strength
If all threads on box connector member engage threads on pin connector member, then maximum thread engagement is achieved, but thread separation occurs during expansion
Solution Approach 1:
The thread connection transitions from a static fully-engaged state to a dynamic configuration during expansion. The disengaged threads provide the necessary degrees of freedom for the connector to dynamically adjust to expansion forces, maintaining connection stability while accommodating dimensional changes in the tubulars.
Data Source
AI summary
A pin-box well tubular connector assembly having pin and box connector members (6, 5) with intermeshing external and internal screw thread profiles is optimized for expansion downhole in a wellbore by: A) configuring the box connector member (5) such that it has at least one thread (10) that does not engage a thread on the pin member (6); and optionally: B) configuring the pin and box connectors (6, 5) such that in axial direction a gap of at least 0.2 mm is present between the external and internal screw thread profiles; and/or C) inserting a swellable dope in the gap between the pin and box connector members (6, 5).